The 3rd Generation Partnership Project (3GPP) is responsible for the standardization of the UMTS (Universal Mobile Telecommunication Service) system, and LTE (Long term Evolution) is now under discussion as a next generation mobile communication system of the UMTS system. LTE is a technology for realizing high-speed packet-based communication that can reach a data rates of about 100 Mbps on the downlink and about 50 Mbps on the uplink.
The 3GPP LTE system will include protocols intended to minimize the loss of data transmitted through the radio link between entities in the network. One of these protocols is known as the radio link control (RLC) protocol used for communication between user equipments in a cell and a controlling node or nodes, e.g. a radio base station(s) of the cell. In LTE, a base station is also known as eNB (enhanced/evolved NodeB) or eNodeB which performs the functions of a conventional radio access network (RNC) node of a UMTS Node B. In addition, eNBs in LTE will interact directly with the core network and with other eNBs.
The 3GPP LTE system will also include a LTE medium access control (MAC) protocol specifying means for a transceiver (or entity), e.g. a transmitter, to notify higher layers of a transmission failure. In order to provide notifications of transmission failures, the MAC layer in LTE comprises a so called Multi-Process Stop-And-Wait HARQ protocol and in accordance with this protocol, a HARQ entity, e.g. in a receiver, is configured to send a positive or a negative feedback at a predefined time in response to each transmission attempt. A positive feedback is also known as an acknowledgement (ACK) whereas a negative feedback is known as a non-(or negative) ACK (NACK). HARQ is therefore generally used for facilitating fast error detection and correction. As an example, a uplink HARQ transmitter interprets a received HARQ NACK as implicit grant allowing the transmitter to perform a retransmission at a predefined time. The feature of notifying higher layers of transmission failure(s) is also referred to as local-NACK since it enables higher layer protocols to trigger a retransmission without relying on higher layer timers or other triggers. This detection mechanism takes into account the HARQ feedback (ACK/NACK) provided by a HARQ receiver to a HARQ transmitter.
According to the prior art 3GPP technical specification TS 36.321, v8.1.0, it is mandatory for the MAC layer to inform a radio resource control (RRC) function (or layer) in the transmitter about a failed HARQ transmission when the HARQ process contained data that are mapped to a common control channel (CCCH). A CCCH is a channel that supports common procedures required to establish a dedicated link with a network. In case data is not mapped to CCCH, the above mentioned specification describes that the HARQ transmitter can be configured to inform the RLC automatic repeat request (ARQ) about said HARQ transmission failure. The prior art specifications thus deals differently with a notification of a HARQ transmission failure depending on whether data is mapped on the CCCH or not. Furthermore, the technical specification defines a method allowing a base station (i.e. eNB or eNodeB or NodeB) to temporarily suspend a planned upcoming transmission from a user equipment (UE). For that purpose, the eNodeB can be configured to send a positive HARQ ACK even though said eNodeB was not able to correctly receive or correctly decode the corresponding HARQ process that is associated with the HARQ ACK. By sending the HARQ ACK, the eNodeB temporarily indicates to the UE that the transmission was successful although it was not. However, after a predefined time duration or after a so called HARQ round-trip-time (RTT) duration, the eNodeB may then issue an uplink grant (for re-transmission) in order to allow the UE to resume the transmission cycle of the suspended cycle. The eNodeB is configured to suspend uplink transmissions in order to e.g. reduce the probability that a retransmission from the UE collides with a transmission attempt from another UE. In other words, it is considered important for a eNodeB to be able to suspend transmissions since the occurrence of a collision is likely to result in a loss of the packets or signals transmitted from UEs involved in the collision.
In the above mentioned technical specification, the local NACK mechanism used to deal with detection of a transmission failure is also known as the HARQ process. The prior art HARQ process described is configured to mainly base it decision on the HARQ failure detection if:
(a) a predetermined maximum number of allowed transmission has been performed for this process and
(b) no HARQ ACK is received for this process.
A drawback with the solution described above is that the HARQ process cannot guarantee a proper/correct detection of a HARQ transmission failure. This is the case, for example, if the HARQ receiver in the eNodeB decides to (temporarily) suspend an uplink transmission from a UE by sending it a positive HARQ ACK for suspension, even though the eNodeB was not able to decode or receive the HARQ process correctly. Thus since the HARQ ACK for suspension has been sent to the UE, the failure detection mechanism (e.g. the local NACK) as currently defined (see above) will interpret a suspended HARQ process as successfully completed. This will therefore cause, in addition to an improper functioning of the HARQ process also an improper utilization of the UE buffer leading to an unnecessary increase in data latency. Note that this is true even if, as explained earlier, the eNodeB resumes (or restarts) the HARQ process due to suspension by sending a HARQ NACK in a following predefined time interval.